1 / 31

Lecture 10: Token Ring and FDDI Networks

Lecture 10: Token Ring and FDDI Networks. Homework for Chapter 2: All problems, particularly time lines for sliding window protocol Exam 2: October 16, 2000. Token Ring Review. Shared medium similar to ethernet Distributed algorithm controls transmission All nodes see all frames.

catherine-sallas
Download Presentation

Lecture 10: Token Ring and FDDI Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 10: Token Ring and FDDI Networks • Homework for Chapter 2: All problems, particularly time lines for sliding window protocol • Exam 2: October 16, 2000

  2. Token Ring Review • Shared medium similar to ethernet • Distributed algorithm controls transmission • All nodes see all frames Token=small (24 bit) circulating frame To send: Remove token and send frame Sender: removes message when it comes around and reinserts token

  3. Key Concept • Token Holding Time (THT)>transmission time of a packet • Token Rotation Time (TRT)< ActiveNodes x THT+RingLatency Note: TRT is load dependent

  4. Fiber Distributed Data Interface (FDDI)

  5. Single Attachment Stations (SAS) attached to a concentrator (DAS)—Star-like topology

  6. FDDI physical properties • 100 Mbps—bit time is only 10 ns • Network adaptor buffers-9-80 bits-retransmit when half full • Queuing delay=50 ns for 10 bit buffers • Up to 500 stations • 2 km between stations (propagation delay=10 ms) • 100 km ring circumference--200 km total fiber length • 4B/5B encoding • Packet size=18,200 bytes

  7. FDDI physical properties (cont.) • Complete Ring: • Ring Latency=24 (10 ns)+500*50 ns+0.5 ms=0.53 ms • Packet transmission time=1.45 ms • Every node should see a valid transmission (token or data frame) every 1.98 ms (or less). This is called the idle time • Broken ring: • Ring Latency =24 (10ns)+1000*50ns+1.0ms=1.05 ms • Idle time=2.5 ms

  8. Key Parameters • Target token rotation time (TTRT)-upper bound to TRT as seen from any node • So, TTRT is a measure of the maximum possible delay as seen by each station • TTRT is negotiated—the station with the most sensitive application sets TTRT (more later) • Measured TRT-every station measures current value of TRT

  9. Media Access Algorithm(Timed Token Algorithm) • If Measured TRT > TTRT, the token is delayed—station is not permitted to send • Measured TRT < TTRT, station can send TTRT-Measured TRT=THT • Ideally, this algorithm provides feedback needed to keep the ring from being overloaded

  10. Access Problems • Station are allowed to start packets that cause THT> TTRT-Measured TRT • If you are downstream from such a node, you may never be able to send your packets • Two traffic categories • Synchronous—e.g. time sensitive-Total synchronous traffic limited TTRT per ring rotation • Asynchronous-governed by Timed Token Algorithm

  11. Worst Case Performance • Token Rotation Time=2TTRT • Does not happen on successive rotations

  12. FDDI Token Maintenance • Recall idle time of a broken ring is 2.5 ms • Stations send claim if idle longer than 2.5 ms • Claim contains a bid for TTRT that is the maximum that is acceptable to by sending station • Bid is passed on by nodes with higher TTRT-they reset their TTRT to the bid value • Bid is replaced by nodes with lower TTRT requirements • Eventually, TTRT is set to the largest value that satisfies all stations.

  13. FDDI frame format

  14. Wireless LAN - 802.11 • LAN - Local Area Network. A network based on any physical network technology that is designed to span distances of up to a few thousand meters. • IEEE 802 LAN-Shared mediumpeer-to-peer communications network that broadcasts information to all stations to communicate

  15. Wireless LAN - 802.11 • OSI Layer 1 - Physical • Encoding/Decoding • Preamble generation/removal • Bit transmission/reception • OSI Layer 2 - Data Link • Medium Access Control/Arbitration • Addressing • Protocol Data Unit/Frame

  16. Wireless LAN - 802.11 • Design issues • Distance • Performance • Reliability • Security • Administration • Scalable

  17. Wireless LAN - 802.11 • Technology • LAN Emulation • Frequency Hopping • Direct Sequencing • Collision • Distribution • Frame Format • Other

  18. Wireless LAN - 802.11 • Frequency Hop Spread Spectrum • 2.4Ghz, 1 and 2 Mbps transmission • Hop over 79 channels (N.America) • Pseudo-random hopping • Interference Immunity

  19. Wireless LAN - 802.11 • Direct Sequence Spread Spectrum • 2.4Ghz, 1 and 2 Mbps transmission • 11 Chip Barker Sequnce • Interference Immunity

  20. Wireless LAN - 802.11 • Baseband Diffuse Infrared • 1 and 2 Mbps transmission • Interference Immunity • Light • Reflection

  21. Wireless LAN - 802.11 • Baseband Diffuse Infrared • 1 and 2 Mbps transmission • Interference Immunity • Light • Reflection

  22. Wireless LAN - 802.11 • Direct Sequencing • Chipping Code • Spread signal across frequency • Increase in bandwidth determined by bit size of chipping code • 802.11 chipping code 11-bits

  23. Four-bit chipping sequence

  24. Wireless LAN - 802.11 • Collision Avoidance • Unlike Ethernet, not all nodes can “see” each others signal • Use of RTS/CTS/ACK handshake between sender and receiver

  25. Example of a wireless network

  26. Wireless LAN - 802.11 • Components • Access Point • Central wireless base Unit • Client • Remote Node • Distribution System • Interconnecting LAN (Like Ethernet)

  27. Access points connected to a distribution network

  28. Node Mobility

  29. IEEE 802.11 frame format

  30. Wireless LAN - 802.11 • Other related Topics • IEEE 802.11b - 11Mbps Wireless LAN • Currently only DSS support from vendors • IEEE 802.11a - Future (51Mbps?) Wireless LAN

  31. Wireless LAN - 802.11 Other References (outside of class text): http://grouper.ieee.org/groups/ 802/11/Tutorial/index.html Stallings, W “Data and Computer Communications - 5th ed.”, Prentice-Hall, 1997

More Related